This invention pertains to the art of combustion apparatus and, more particularly, to a gas generator. The invention is particularly applicable to wood gas generation and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other carbon-based fuel environments and applications.
In the past, two stage combustion processes have been developed for converting high moisture content carbon-based fuels into energy without undue pollution of the atmosphere. Typically, the first stage converts the fuel into two components, a combustible gas and residual ash. The second stage combusts the gas to release heat energy. The generated gas burns as cleanly as natural gas, so that expensive clean-up equipment is unnecessary. In fact, the combustion of the gas requires less air than conventional single stage combustion processes for similar fuels. Therefore, the combustion efficiency of the two stage process is higher.
Generally, a gas generator converts a solid carbon-based fuel into a combustible gas through continuous reaction with an oxygen-carrying gas. The reaction may be broken down into a sequence of reaction zones defined along the direction of gas flow such as an ash zone followed by an oxidation zone, a reduction zone, devolatilization and preheating zones. When wood or bark is used as the fuel, usually as a by-product of a saw mill or papermaking industry, the wood waste fuel is used to provide energy for process. The moisture content of wood and bark is generally high, such that the heat required to heat the fuel and evaporate the moisture is also quite high. The parameters must be closely controlled in order to assure combustion without injecting an excess amount of air into the reaction chamber.
By way of example, U.S. Pat. Nos. 4,300,460 issued Nov. 1981 to Frank Lamb, et al.; 4,384,534 issued May 1983 to Frank Lamb, et al.; and 4,388,876 issued Jun. 1983 to John Burton illustrate the various apparatus utilized by industry. The combustion apparatus illustrated in the enumerated patents, as well as in other prior art units, are not designed to produce gas as an output. Rather, these units burn the gas immediately in a combustion chamber that is integrated closely with the first stage gas generation equipment. These two stage units, when considered as a whole, produce energy in the form of hot products of combustion. Additionally, the above-noted design configurations are limited to cylindrical chambers which, in turn, limits the size and efficiency of the units to approximately 60,000 lb. of steam generation per hour. Another drawback is encountered with systems similar to U.S. Pat. No. 4,384,534 which has a radial rabble arm for ash removal. The radius length of the rabble arm is limited by both mechanical and effective ash removal constraints which again limit the size of the units.
It has, therefore, been deemed desirable to design a wood gas generator which overcomes the above-noted deficiences and others. By way of example, a system having a reduced capital cost that reduces the amount of power consumption, as well as eliminating environmental clean-up equipment such as scrubbers or the like, would be greatly desired. In addition, separation of a generated clean gas for direct combustion within boilers, kilns, or similar heat exchange equipment and for direct powering of gas turbines and the like is desirable. The subject invention is deemed to meet these needs and others in an economical manner.